1) Field of the Invention
The present invention relates to an orthogonally excited-type laser oscillator which has a structure capable of stably maintaining the output of a laser beam and the quality of a beam mode, by keeping a constant positional relation such as parallelism or imperfect alignment of a pair of optical resonators even if an oscillator case is deformed due to heat.
2) Description of the Related Art
A gas laser oscillator generally includes a discharge tube filled with laser gas to excite the laser by discharging, and an optical resonator having two mirrors disposed on opposite sides of this tube. When a large amount of heat is produced in the tube when the laser is oscillated, a part of the heat is transmitted to the optical resonator or a base plate which supports the discharge tube or the optical resonator. These devices are deformed by heat, which results in causing a disorder in the parallelism of the pair of optical bases constituting the optical resonator, or positional displacement between the axis of the optical resonator and the axis of the oscillator case. Further, the optical resonator itself causes a difference in the thermal expansion between components, such as a bar of an end plate of a flame, relative to each other due to a change of the outside temperature. This may also cause positional displacement of the optical resonator. The displacement of the optical resonator brings about a disorder in the mirror alignment, to thereby make the laser output and the beam mode unstable. Therefore, in order to cope with the positional displacement of the optical resonator due to the influence of heat, laser oscillators having various constructions have been proposed.
As the invention relating to the conventional laser oscillator, there is a conventional art disclosed in Japanese Patent Application Laid-Open No. 2000-183425 shown in FIG. 12. In this conventional art, a front optical base 9 and a rear optical base 7 are disposed on the opposite sides of an oscillator case 1. A partial reflection mirror is fixed to the front optical base 9 and a total reflection mirror is fixed to the rear optical base 7. The front optical base 9 and the rear optical base 7 are firmly connected with each other by support rods 112 to 114 extending in the traveling direction (in the direction of optical axis) of three laser beams, one in the lower part and two in the upper part, so that the partial reflection mirror and the total reflection mirror are fixed parallel with each other on the same optical axis. The support rods 113 and 114 on the upper side of the oscillator case 1 are connected to the central portion in the direction of the optical axis on the upper face of the oscillator case 1 with the axially central portion being connected by brackets 120 and 121, respectively. The support rod 113 located on a blower side where there is little thermal deformation is perfectly fixed to the oscillator case 1 by the bracket 120, while the support rod 114 located on the other side at a high temperature is movably connected to the oscillator case 1 by the bracket 121 provided on a slide base 122 whose axial movement and vertical movement are restricted. That is, the bracket 121 can slide on the slide base 122 in the left and right direction as shown by the arrow. The support rod 112 in the lower part is not connected to the oscillator case 1 by a bracket, but only the opposite ends of the support rod 112 are fixed to the optical bases 9 and 7. The portions where the laser beam passes between the oscillator case 1 and the rear optical base 7, and between the oscillator case land the front optical base 9 are connected by bellows, respectively.
In the above-described conventional art, it is possible to suppress a change in the positional relation between the two optical bases 7 and 9 due to a temperature distribution of the laser medium gas, by the support structure using the three support rods 112 to 114 and the brackets 120 and 121. However, since the oscillator case 1 thermally deforms freely due to the temperature distribution of the laser medium gas, the position or the angle at the opposite ends thereof changes. As a result, the positions of the bellows fitted to the opposite ends of the oscillator case 1 change. Generally, the rigidity of the bellows in the deviation direction of the core is very large as compared to the axial rigidity, and a harmful reaction force occurs by the positional displacement of the bellows. By this reaction force, the structure of the optical resonator is deformed, thereby the positional relation between the two optical bases 9 and 7 collapses. Such positional displacement between the optical bases 9 and 7 makes the laser output or the beam mode unstable.